Jul 17, 2012
Algorithm investigates different stable states of cantilever oscillation in AFM
Atomic force microscope (AFM) cantilevers can oscillate in different stable states, even under identical experimental conditions. The reason is the complicated interplay between the repulsive and attractive interaction forces between the tip of the cantilever and the sample surface. Repulsion and attraction are weighted differently in the different oscillation states, which can be distinguished by the amplitude and phase lag of the oscillation. The choice of the state of oscillation has a strong influence on the resulting images.
A systematic study published recently in the journal Nanotechnology now shows the influence of experimental parameters on these resulting states. This insight enables the experimentalist to choose the desired interaction forces for scanning. Test measurements on semicrystalline polymers show, for instance, an improved resolution while scanning in the predominantly attractive regime.
The existence of different stable oscillation states of the AFM cantilever in the intermittent contact mode has been known for a long time. But the influence of experimental parameters such as cantilever stiffness or excitation amplitude is only empirically known. In the case of small dissipation, when the motion of the cantilever stays harmonic, the researchers were able to systematically study the influence of such important parameters using simulations based on a generic force model.
For the first time a coexistence of up to three stable oscillation states was found. The case of the so-called attractive regime is especially interesting for studying the morphology of soft samples while avoiding strong intrusion by the tip of the cantilever.
Full details can be found in the journal Nanotechnology.
About the author
Thomas Henze did his PhD in the physics department of Martin-Luther-University Halle-Wittenberg, Germany, in the experimental polymer physics group under the supervision of Thomas Thurn-Albrecht. He is now an application scientist at the AFM manufacturer JPK Instruments. As a senior scientist Klaus Schröter leads the AFM activities in the group. The investigation of structure formation processes in polymers by AFM and scattering experiments is one of the main topics of research in the group.